1. Field of the Invention
The present invention is related to the field of signal transmission. More specifically, the present invention is a method and apparatus for switching input terminals based on a device""s capability.
2. Related Art
Use of digital interfaces is a trend in signal transmission, as a result of recent developments in digital signal processing technologies. Analog video and audio signals are digitized and coded, or compressed, before being transmitted. Various types of compression techniques, including DVI (Digital Video Interactive) and MPEG (Motion Picture Experts Group) compression, have been developed to achieve high-performance digital signal transmission. Standards developed for digital interfaces, such as IEEE1394, allow digital signals in various formats to be transmitted through a single digital interface. Such standards, however, do not regulate the formats in which the signal is coded, nor control the transmission path through which the signal is transmitted.
It is vital to ensure that a device that receives a digital signal in a particular format is capable of decoding it to recover an original signal from it. This requirement was relatively easy to satisfy when digital signals were coded and transmitted in a limited number of formats such as the DV (Digital Video) format. Development of digital signal processing technologies has led to different formats, and distinctive modes exist for some formats with regard to the transmission speed and bandwidth of the signal. Devices that receive and use transmitted signals are not necessarily provided with decoders corresponding to the various formats, due to economic reasons. One problem that has emerged is that an incoming signal is not always received in a usable format, and if this is the case, a device using the signal cannot decode the transmitted digital signal. A digital TV that can process digital signals exclusively in the format based on the MPEG Standard, for example, cannot process signals coded in the DV format or the DSS (Digital Satellite System) format.
In addition to the differences between the coding formats of digital signals, signals are not always transmitted in a digital format but also in an analog format, particularly in a transition period from analog to digital, while both formats are in use. In other words, analog signals can co-exist with digital signals.
Some transmitters and receivers, having both analog and digital interfaces, are designed to process digital signals as well as analog. In order to transmit an analog signal to such a device, the signal has to be transmitted through the analog interface. Otherwise the signal cannot be transmitted to the receiver. It is vital, therefore, to select an appropriate transmission path, i.e., the digital interface or the analog interface, depending upon the type of the signal, digital or analog.
For the foregoing reasons, there is a need for a method for switching input terminals based on a device""s capability.
The present invention is directed to a method and apparatus that satisfies the need for switching between input terminals based on a transmitted signal format.
Whether or not a device is receiving a digital signal at a digital input terminal in a usable format is examined; and an analog input terminal is selected to receive an analog signal unless the digital signal is being provided in the usable format.
More specifically, the method includes receiving a digital signal at a digital input terminal of a device, receiving an analog signal at an analog input terminal of the device, examining whether or not the digital signal is in a usable format for the device, and selecting the digital signal if the digital signal is in the usable format, otherwise selecting the analog signal, as an input for the device. The digital signal and the analog signal may be supplied to the device simultaneously.
An apparatus to which the present invention is directed includes a digital input terminal which receives a digital signal, an analog input terminal which receives an analog signal an IEEE1394 interface coupled with the digital input terminal, a decoder coupled with the IEEE1394 interface, a memory and a selector which selects the digital input terminal if the digital signal is in a usable format for the apparatus, otherwise it selects the analog input terminal. The selector may include a controller for examining whether or not the decoder is capable of decoding the digital signal, and a switch controlled by the controller so as to select the digital input terminal if the decoder is capable of decoding the digital signal, otherwise to select the analog input terminal.
According to the present invention, it is possible to supply a usable signal in an analog form even though a digital signal is received in a format that the device cannot decode. Therefore, a user of digital equipment does not have to manually change the input terminal.